The present invention relates to a process and to a device for implementing this process making it possible to ensure maintenance on a data transmission network without physical and momentary breaking of the network, these data being furthermore conveyed on a two-wire network.
It is intended more particularly to allow the verification and monitoring of the communication protocols (analysis of signals, analysis of perturbations, on-oscilloscope display, analysis on the _LABVIEWxe2x80x3 platform, analysis of frames, protocol analysis (Transpac, Internet etc.), error metering, qualification, CRC extraction, observations/monitoring, levels, jumps in levels, outages and brownouts etc.) exchanged between two installations linked by a two-wire data transmission network operating in Half Duplexxe2x80x3 and/or _Full Duplexxe2x80x3 mode without resorting to a differential transformer, whilst guaranteeing negligible line attenuation of the order of in particular 0.5 db/600 ohms (impedance to be matched to the bit rate of the line), both in analogue and digital technology.
The known processes have been developed for data transmission networks based on a four-wire architecture, two wires being reserved for sending, two wires being reserved for receiving. With this type of technology, measurement apparatuses comprising a High Impedance input allow the extraction of the signals, without perturbing the exchanges in progress. Depending on how they are hooked up (in parallel on the Send pair or in parallel on the Receive pair), observation will be carried out with regard to the sending of the data or with regard to their reception.
It is easily understood that in a two-wire technology, whether analogue or digital, the two wires convey both a send message and a receive message, it is impossible to introduce a protocol monitoring apparatus without breaking the network. Now, hitherto all the known apparatuses require an interruption, albeit brief, of the network in order to hook up or unhook the device between the installations to be monitored.
The present invention aims to alleviate these drawbacks by proposing a process and a device for implementing this process, which permits the acquisition of signals and their subsequent interpretation, without breaking the line in a two-wire data transmission network.
For this purpose, the process aimed at the extraction of electrical signals emanating from the two ends of a 2 wire link between two installations exchanging data is characterized in that a probe comprising an attenuation cell is plugged in on either side of a break point situated on the line pair, then the connections thus established are isolated in such a way as to transfer the signals to the attenuation cell, the attenuation cell is activated by progressive withdrawal of the active components, high-impedance signals are tapped off at the two ends of the attenuation cell, and signals which are images of the electrical signals dispatched by one or other of the ends of the line pair are obtained as output from the attenuation cell, after analogue calculation based on subtraction of the signals and multiplication by a constant which is directly related to the value of the attenuation of the cell.